The striker has been at the centre of an international tug-of-war between La Roja and the nation of his birth but has opted to play for Vicente Del Bosque's side
The 25-year-old has been at the centre of a tug-of-war between La Roja and the country of his birth and was handed a call-up by Luiz Felipe Scolari for Brazil's upcoming friendlies with Honduras and Chile in November.
But after weeks of speculation, Costa, who was granted Spanish citizenship in July, has confirmed his desire to represent Spain by signing an official declaration, revealed in statement on the national side's official website.
"On the morning of Tuesday, November 29, the Brazilian-Spanish player Diego Da Silva Costa "Diego Costa" has come to the notice Serrano 30, where he proceeded to sign a letter which states his intention to play for Spain.
"The letter was given to D. Julio Cesar Avelleda, secretary general of the Confederation Brasileira de Futebol (CBF), and confirms his desire to be available to the Spanish national coach Vicente del Bosque, as of right now.
"Thus, Diego Costa will play for Spain in the next games for the month of November, if deemed appropriate by the national team coach."
Costa is arguably Europe's most in-form striker having struck 11 times in his first 10 Liga games this season.